This invention relates to the production of a substrate having components mounted thereto and more particularly to the technology of carrying out an inspection by image processing, either during or after a production process therefor, of the lands, the soldered parts and the mounted components on the substrate that is being produced or has been produced.
The present inventors have previously developed an apparatus for automatically inspecting soldered portions on a substrate by the image processing technology making use of the mirror reflection property of such soldered portions, as described in Japanese Patent Publication Tokko 6-1173. The optical system of this previously developed inspection apparatus comprises three circular ring-shaped light sources having different diameters and a two-dimensional color camera (hereinafter simply referred to as a camera). These three light sources are respectively adapted to emit a beam of red, green and blue light, and the camera is disposed at a position corresponding to the center of these light sources with its optical axis vertically oriented. With an inspection apparatus thus structured, each of the light sources is positioned so as to have a different angle of elevation from the position of a solder portion to be inspected. Each beam of light projected onto the surface of the solder portion undergoes a mirror reflection but the kind of mirror-reflected light received by the camera changes according to the sloping angle of the light-reflecting surface of the solder. Thus, the three colors of the light sources become distributed on the solder portion of the obtained image along the direction in which this sloping angle changes. Thus, if the pattern of each color that would appear on the image of a well-shaped solder surface is preliminarily registered and compared with color patterns that are actually obtained from a target surface, it is possible to judge the quality of the target surface for inspection.
With an illumination device of the type described above and adapted to project light beams of three primary colors, however, the range of angle in which the light beam of each color is projected is fixed and hence the corresponding relationship between each color and the angle of slope also becomes fixed. As a result, if the slope of a solder fillet becomes very steep, it becomes difficult to display the color distribution reflecting the change in this slope. Accordingly, a color change may not be obtained from the image corresponding to a fillet and it becomes difficult to detect its slope.